PROJECT SUMMARY/ABSTRACT Current treatments for Alzheimer's disease are minimally effective in slowing the progression because they can only be prescribed once symptoms of the disease are reported. By this time, irreversible neuron death and brain atrophy have occurred. Finding new, earlier biomarkers of Alzheimer's disease is imperative to developing new treatments that can target early prevention of neuropathological changes. Naturalistic tasks, including complex, everyday tasks and performing a cognitive task while walking (i.e., dual-tasking), require coordination of executive function, working memory, and visuomotor coordination, which are the cognitive functions that are typically impacted early on in Alzheimer's disease. Subtle declines in cognitive function may impact cognitive processing, visuospatial attention, and motor function, leading to impaired ability to perform these naturalistic tasks well before most patients report symptoms and thus may provide new, earlier biomarkers of high risk of developing Alzheimer's disease. Therefore, the goals of this project are to determine if measures of visuospatial attention and gait smoothness during performance of complex, everyday tasks involving walking can differentiate between older adults at high risk of developing Alzheimer's disease (pathological levels of beta amyloid accumulation), low-risk older adults, and young adults (Aim 1), and identify if dual-task costs on gait, visuospatial attention, and cognition can differentiate between high-risk older adults, low-risk older adults, and young adults (Aim 2). Thirty high-risk older adults (?70 to ?85 years), 30 low-risk older adults ((?70 to ?85 years), and 30 young adults will be assessed in 5 conditions: simulated grocery shopping task, walking on uneven ground task, cognitive single-task (performing an inhibition-executive function and a working memory task while seated), gait single-task (walking at fastest comfortable speed and at fastest comfortable speed while stepping over obstacles, without any simultaneous cognitive task), and dual-task walking (walking while performing cognitive tasks). This project will employ the concurrent recording of gait, eye movements, and cognitive performance to identify how gait smoothness, visuospatial attention, and dual-task costs on gait, visuospatial attention, and cognition can differentiate those at high- versus low-risk of developing Alzheimer's disease while performing naturalistic tasks. The proposed project is a supplement to B-NET (R01AG052419), a longitudinal study examining beta amyloid accumulation, neurocognitive function, and mobility functioning in older adults. Adding the proposed assessments to the data already collected in the parent study will provide an innovative examination of if a fine-grained analysis of cognitive processing, visuospatial attention, and smoothness of gait during naturalistic everyday tasks can serve as an early biomarker of risk of developing Alzheimer's disease.